ruby: functional access updates to network test protocol

I had forgotten to change the network test protocol while making changes to
ruby for supporting functional accesses. This patch updates the protocol so
that it can compile correctly.

src/mem/protocol/Network_test-msg.sm

@@ -41,7 +41,11 @@ structure(RequestMsg, desc="...", interface="NetworkMessage") {
   DataBlock DataBlk,           desc="data for the cache line";
   MessageSizeType MessageSize, desc="size category of the message";
 
-  void functionalWrite(Packet *pkt) {
+  bool functionalRead(Packet *pkt) {
+    error("Network test does not support functional accesses!");
+  }
+
+  bool functionalWrite(Packet *pkt) {
     error("Network test does not support functional accesses!");
   }
 }